ONE. THE BASICS
What are emotions, and why do we have them?
No one definition for emotions exists. Many dictionaries refer to "feelings" or "moods" when defining the word; this further begs the question of what they are. Scientists who attempt to study emotional phenomena characterize them in terms of their particular interest, and thus definitions change depending on whether the scientist is studying the biologic, psychological, or social basis of emotions. This, of course, further complicates the understanding of emotions.
Historically, the mind was thought to be separate from the body and part of the soul. In fact psyche is the Greek root for "soul." With the advent of a more scientific understanding of the brain and mind, some scientists attempt to liken the mind to software and the brain to hardware. In actuality, however, it is not quite so simple. A simultaneous change in brain activity accompanies every change in thought, feeling, perception, or action. Today, scientists increasingly appreciate the fact that no sharp demarcation exists between the brain and the mind.
Despite the fact that mind and brain are essentially unified, drawing a boundary between the two allows for practical differences between them to be conceptualized in everyday lives. For example, such a boundary permits distinction between acts and motives. Distinguishing acts from motives helps with negotiation through everyday social interactions. For example, consider the feelings generated when standing in line and having your toes stepped on. With the immediate sensation of pain comes the feelings of shock, surprise, and probably anger. The feelings experienced are immediately followed by an assessment of the person's motives or state of mind. Action on that assessment is guided by feelings. Emotions therefore serve to engage the body to act in some manner. The manner on which an action is taken usually carries some survival value to a given individual.
Thus lack of emotions could be likened to the lack of physical pain sensation. This lack would cause numbness to the environment and thus problems in interacting with it appropriately. Without the ability to feel anger, joy, sorrow, fear, or love, humans would be incapable of generating priorities to action. Emotions help to prioritize—to decide when to act and when not to act. Without such abilities, choosing between arrays of decisions that are confronted on a daily basis would be unfeasible.
What is the difference between thoughts and feelings?
Emotions or feelings are often distinguished from thoughts. Emotions are typically considered the irrational or animal part of humans, whereas thoughts are the rational part. Strong feelings such as anger, joy, fear, and sadness result in behaviors that do not seem to always serve one's interests. Thoughts are the words in the head that give mental content to hopes, dreams, and desires and allow for reasoning and weighing of options so that an assessment of consequences can be made before actions are taken.
Scientists now know through the use of experiments and clinical observation that thoughts, feelings, and perceptions coexist as a unified whole and cannot be easily teased apart. Thus every thought is given a
Emotions help to prioritize— to decide when to act and when not to act.
positive or negative emotional valence that allows us to prioritize our actions on those thoughts. Evidence in support of that comes from the fields of neurology and the computer sciences. Neurologic studies show that people who suffered brain damage that cuts thoughts off from feelings are unable to prioritize a list of preferences and act on them to achieve even the simplest of goals. Even simple tasks, such as choosing a restaurant, become impossible because of entrapment in a never-ending cost-to-benefit analysis of numerous and conflicting options. Similarly, computer programmers have struggled to develop simple algorithms  that can generate decisions, appropriately weighing all costs and benefits without becoming literally buried underneath an infinite loop of ones and zeros. Emotions are therefore a necessary piece that work with thoughts in decision making and hence planning of future goals.
-  referring to all matters of the nervous system that includes brain, brainstem, spinal cord, and peripheral nerves. Problems with specific, identifiable, pathophysiologic processes are generally considered to be neurologic as opposed to psychiatric. Problems with elements of both pathophysiologic and psychiatric manifestations are considered to be neuropsychiatrie
-  a sequence of steps to follow when approaching a particular problem.